In an impulse type display device such as a CRT (Cathode Ray Tube), as for individual pixels, each individual pixel repeats alternately a lightening period in which an image is displayed and a non-lighting period in which an image is not displayed. For example, in a case where a moving image is displayed, an afterimage of a moving object does not occur to human eyes because the non-lighting period is inserted at the time when an image of one screen is rewritten.
On the other hand, in a hold type display device that employs TFTs (Thin Film Transistors), a luminance of each individual pixel depends on a voltage that is held by each corresponding pixel capacitor. The voltage that is held by the pixel capacitor is kept for one frame period, once rewritten. In the hold type display device, a blurring phenomenon (moving image blur) occurs when a moving image is displayed. This moving image blur is caused by pursuit of a displayed moving body with eyes (eye pursuit).
Accordingly, in a hold type display device such as an active matrix type liquid crystal display device, a moving image blur occurs at the time of a moving image display. On this account, a technique for improving this moving image blur is proposed.
For example, Patent Document 1 discloses, as a method of improving a trailing afterimage mentioned above, a method of converting a display of the liquid crystal display device into a (pseudo-)impulse display by insertion of a period in which a black display is performed (hereinafter, referred to as “black insertion”) in one frame period.
According to Patent Document 1, as illustrated in FIG. 11, for example, in the case of a liquid crystal display panel that includes 480 scanning lines (gate lines), the gate lines Y1 through Y480 are sequentially activated, according to respective timings that are slightly shifted one another, for writing image signals into respective pixel cells during one frame period. The one frame period is completed, when all of the 480 gate lines are activated and an image signal is written into each pixel cell. In this operation, after approximately ½ frame period from the activation for writing the image signal, the gate lines Y1 through Y480 are activated again so that an electric potential for displaying black is supplied to each pixel cell via a data line X. This causes the each pixel cell to be in a black display state.
That is, each gate Y becomes high level twice in different times of one frame period. In response to first selection of the gate line Y, the each pixel cell displays image data for a predetermined period. In response to subsequent second selection of the gate line Y, the each pixel cell is forced to perform a black display. In this way, an image display period and a black display period are provided in one frame period. This allows a hold type drive display state to approach a pseudo impulse type drive display as in a CRT. This makes it possible to improve image quality deterioration caused by motion blur that occurs at the time of a moving image display.
Although contrast is excellent in a vertical alignment mode (VA mode), a gamma curve at the front does not agree with a gamma curve at an oblique viewing angle. Accordingly, a whole screen looks white (excessively bright) when viewed at an oblique viewing angle, compared with a case where the screen is viewed at the front. As a technique for reducing the excess brightness at the oblique viewing angle, for example, Patent Document 3 splits one picture element into a plurality of sub-picture elements (multi-picture element structure) and sets respective luminances of the sub-picture elements so that the luminances differ from each other (this technique is called a multi-picture element technique or an area coverage modulation technique).
[Patent Document 1]
    Japanese Unexamined Patent Publication No. 109921/1999 (Tokukaihei 11-109921 (published on Apr. 23, 1999))[Patent Document 2]    Japanese Unexamined Patent Publication No. 345973/2005 (Tokukai 2005-345973 (published on Dec. 15, 2005))[Patent Document 3]    Japanese Unexamined Patent Publication No. 62146/2004 (Tokukai 2004-62146 (published on Feb. 26, 2004))